This ongoing training program prepares graduate students and postdoctoral fellows for biostatistical and epidemiological research directed against the HIV epidemic. The program emphasizes strong training in statistical methodology, epidemiology, and related biologic areas. Students majoring in Biostatistics minor in Epidemiology and vice versa. Both have a second minor in a related field such as virology, biology, health policy, population sciences, or behavioral science. The overall objective of the training program is to combine strong methodologic training with an extensive practical exposure to relevant problems and an introduction to specialized research on problems important to combating the HIV epidemic. The presence of expertise in virology, microbiology, and health care issues at the School adds to the unique environment for this training program. The Biostatistics and Epidemiology faculties are extensively involved in methodologic and collaborative research in HIV-related problems. Members of the Biostatistics Department form the Statistical Center for the AIDS Clinical Trials Group within the Center for Biostatistics in AIDS Research, and are the Core Biostatistics Center for the Harvard AIDS Institute. Members of the Departments of Epidemiology and Biostatistics are jointly involve din epidemiological studies in Mexico, Greece, and Japan as well as the national AIDS research program. This provides the trainees with a very rich environment to pursue their research. To facilitate student participation in these research activities, the Department of Biostatistics sponsors faculty-student "working groups" which meet biweekly to discuss ongoing research. During the 1998-1999 academic year, there are separate working groups in the areas of Bayesian methodology, computing, environmental statistics, nutrition research, genetic epidemiology, HIV, longitudinal data, measurement error, psychiatric biostatistics, quantitative issues, cancer research, risk and decision analysis, semi-parametric methods in biostatistics, statistical issues is new drug development, and statistical methods in epidemiology. Experience in the last ten years has taught us what motivates the students to engage in interesting and useful training and research.